CN105801109A - Microwave dielectric ceramic Li2Mg2TiO5 low in loss, stable in temperature and low in dielectric constant - Google Patents

Abstract

The invention discloses application of rock-salt-structured composite oxide Li2Mg2TiO5 as a microwave dielectric ceramic stable in temperature and low in dielectric constant and a preparation method of the rock-salt-structured composite oxide Li2Mg2TiO5.The preparation method comprises the steps of 1, weighing and compounding original powder of Li2CO3, MgO and TiO2 with the purity being 99.9% (weight percentage) or above according to the composition of Li2Mg2TiO5; 2, conducting wet type ball milling and mixing on the raw materials for 8 hours, wherein ethyl alcohol absolute serves as a ball milling medium, and after the raw materials are dried, conducting presintering for 4 hours in air atmosphere; 3, adding binder to powder obtained in step 2, conducting granulation, then compressing the powder for formation, and finally conducting sintering for 4 hours in air atmosphere at the temperature of 1200-1300 DEG C, wherein a polyvinyl alcohol solution with the mass concentration being 5% is adopted as the binder, and the adding amount of polyvinyl alcohol accounts for 3% of the total mass of the powder.The ceramic prepared through the method is good in sintering performance, the dielectric constant reaches 12.3-14.7, the quality factor Q*f of the ceramic is as high as 72,000-85,000 GHz, the temperature coefficient of the resonance frequency is low, and extremely high application value is achieved industrially.

Description

Low-loss temperature-stabilized dielectric constant microwave dielectric ceramic Li2Mg2TiO5

Technical field

The present invention relates to dielectric ceramic material, particularly relate to for manufacturing ceramic substrate, the resonance that microwave frequency uses Dielectric ceramic materials of microwave device such as device and wave filter and preparation method thereof.

Background technology

Microwave dielectric ceramic refers to be applied in microwave frequency band (mainly UHF and SHF frequency range) circuit as dielectric material And complete the pottery of one or more functions, modern communication is widely used as resonator, wave filter, dielectric substrate and medium The components and parts such as wave circuit, are the key foundation materials of modern communication technology, in portable mobile phone, automobile telephone, nothing The aspect such as rope phone, television satellite accepter and military radar has highly important application, small-sized at modern communication instrument Change, integrated during just playing increasing effect.

Just have tried to be applied to dielectric substance microwave technology in the world from late 1930s, and prepare TiO₂Microwave dielectric filter, but its temperature coefficient of resonance frequency τ_ƒToo greatly cannot be practical.Since the seventies in last century, open Begin the large-scale development to medium ceramic material, according to relative dielectric constant ε_rSize with use frequency range not With, generally the microwave-medium ceramics having been developed that and developing can be divided into 4 classes.

(1) ultralow dielectric microwave dielectric ceramic, main representative is Al₂O₃-TiO₂、Y₂BaCuO₅、MgAl₂O₄With Mg₂SiO₄Deng, its ε_r ≤ 20, quality factor q × f >=50000GHz, τ_ƒ ≤ 10 ppm/°C.It is mainly used in microwave base plate And high-end microwave device.

(2) low ε_rWith the microwave dielectric ceramic of high q-factor, mainly BaO-MgO-Ta₂O₅, BaO-ZnO-Ta₂O₅Or BaO- MgO-Nb₂O₅,BaO-ZnO-Nb₂O₅System or the hybrid system MWDC material between them.Its ε_r=20～35, Q=(1～ 2)×10⁴(under the GHz of f >=10), τ_ƒ ≈ 0.In the microwave communication equipments such as the direct broadcasting satellite being mainly used in f >=8 GHz As dielectric resonance device.

(3) medium ε_rWith the microwave dielectric ceramic of Q-value, it is mainly with BaTi₄O₉、Ba₂Ti₉O₂₀(Zr, Sn) TiO₄Etc. for The MWDC material of base, its ε_r =35 ~ 45, Q=(6～9) × 10³(under f=3～-4GHz), τ_ƒ ≤ 5 ppm/°C.Main It is used in the microwave military radar in 4～8 gigahertz frequency range and communication system as dielectric resonance device.

(4) high ε_rAnd the microwave dielectric ceramic that Q-value is relatively low, in being mainly used in 0.8～4 gigahertz frequency range, civilian movement is led to News system, this is also the emphasis of microwave dielectric ceramic research.Since the eighties, Kolar, Kato et al. in succession find and have studied Perovskite-like tungsten bronze type BaO Ln₂O₃—TiO₂Series (Ln=La, Sm, Nd or Pr etc. are called for short BLT system), composite perofskite Structure C aO Li₂O—Ln₂O₃—TiO₂Series, lead base series material, Ca_1-xLn_2x/3TiO₃It is contour ε_rMicrowave dielectric ceramic, The wherein BaO Nd of BLT system₂O₃—TiO₂Material dielectric constant reaches 90, lead base series (Pb, Ca) ZrO₃Dielectric constant reaches To 105.

It is applied to the dielectric ceramic of microwave frequency band, should meet the requirement of following dielectric property: (1) seriation DIELECTRIC CONSTANT ε_r To adapt to different frequency and the requirement of different application occasion;(2) high quality factor q value or low dielectric loss tan δ are to reduce Noise, typically requires Q × f >=3000 GHz;(3) the temperature coefficient τ of resonant frequency_ƒThe least to ensure that device has Heat stability, general require-10 ppm/ DEG C≤τ_ƒ ≤ +10 ppm/℃.Three performances due to microwave dielectric ceramic Index (ε_rWith Q × f and τ_ƒIt is that the relation of mutually restriction is (see document: the system between microwave dielectric ceramic materials dielectric properties between) About relation, Zhu Jianhua, Liang Fei, Wang little Hong, Lv Wenzhong, electronic component and material, phase March the 3rd in 2005), meet three performances Requiring and the single-phase microwave-medium ceramics of low temperature sintering is considerably less, mainly their temperature coefficient of resonance frequency is the most excessive Or quality factor are on the low side and cannot application request.Research major part to microwave-medium ceramics is by a large amount of real at present The summary of experience tested and draw, does not but have complete theory to illustrate the relation of microstructure and dielectric properties.Therefore, in theory On also cannot predict its microwave dielectric property such as temperature coefficient of resonance frequency and quality factor from the composition of compound and structure. Explore, with exploitation, there are near-zero resonance frequency temperature coefficient (-10 ppm/ DEG C≤τ simultaneously_ƒ ≤+10 ppm/ DEG C) with higher The microwave dielectric ceramic of quality factor be those skilled in the art always thirst for solve but be difficult to the difficult problem succeeded all the time.

For exploring novel microwave dielectric material further, Shanghai University's Bian Kien Giang research group reports A₂BO₃Type rock salt is tied Structure Li₂TiO₃Pottery has Medium dielectric constant (ε_r~ 20) and high quality factor Q × f value (56,000 GHz), its resonance frequency Rate temperature coefficient τ_ƒ(+24.1 ppm/ bigger than normal^oC).Rock salt structure is A_aB_bO_a+bOne of most typical structure of type compound, its knot Structure is the network structure that skeleton is constituted with the oxygen octahedra [BO6] of common rib, and wherein anion B is arranged in cubic closest packing, sun from Sub-A is filled in the octahedral interstices that anion is constituted, and the ligancy of A and B is 6.The polytropy of rock salt structure chemical constituent Illustrate that its microwave dielectric property can be adjusted in a wide range with the adjustability of structure.We are at mutual-through type Li₂Mg_xTiO_3+x(0≤x≤4) system has carried out the research of microwave dielectric property, finds along with the increase of Mg content, and it is humorous Vibration frequency temperature coefficient is gradually lowered, when x=2, it is thus achieved that the microwave dielectric material of temperature coefficient of resonance frequency nearly zero Li₂Mg₂TiO₅。

Summary of the invention

It is an object of the invention to provide one and there is good thermal stability and low-loss dielectric constant microwave dielectric pottery Ceramic material and preparation method thereof.

The chemical composition of the microwave dielectric ceramic material of the present invention is Li₂Mg₂TiO₅。

The preparation method step of this microwave dielectric ceramic material is:

(1) be 99.9%(percentage by weight by purity) more than Li₂CO₃, MgO and TiO₂Starting powder press Li₂Mg₂TiO₅'s Composition weighs dispensing；

(2) being mixed 8 hours by step (1) raw material wet ball-milling, ball-milling medium is dehydrated alcohol, at 900 DEG C of air gas after drying Pre-burning 4 hours in atmosphere；

(3) after adding binding agent pelletize in the powder that step (2) prepares, re-compacted molding is finally big at 1200 ~ 1300 DEG C Gas atmosphere sinters 4 hours；Described binding agent uses mass concentration to be the poly-vinyl alcohol solution of 5%, the addition of polyvinyl alcohol Account for the 3% of powder gross mass.

Advantages of the present invention: Li₂Mg₂TiO₅The dielectric constant of pottery reaches 12.3～14.7, the especially temperature of resonant frequency Degree coefficient τ_ƒLittle, temperature stability is good；Quality factor q f value up to 72,000-85,000GHz, can be widely used for various medium base The manufacture of the microwave devices such as plate, resonator and wave filter, industrially has great using value.

Detailed description of the invention

Embodiment:

Table 1 shows 3 specific embodiments and the microwave dielectric property thereof of the different sintering temperatures constituting the present invention.Its preparation side Method as it has been described above, carry out the evaluation of microwave dielectric property by cylindrical dielectric resonator method.

This pottery can be widely used for the manufacture of the microwave devices such as various medium substrate, resonator and wave filter, can meet shifting The technology of the systems such as dynamic communication and satellite communication needs.

Table 1:

Claims (1)

1. the composite oxides as the application of temperature-stable dielectric constant microwave dielectric ceramic, it is characterised in that described The chemical composition of composite oxides is: Li₂Mg₂TiO₅；

The preparation method step of described composite oxides is:

(1) be 99.9%(percentage by weight by purity) more than Li₂CO₃, MgO and TiO₂Starting powder press Li₂Mg₂TiO₅'s Composition weighs dispensing；

(2) being mixed 8 hours by step (1) raw material wet ball-milling, ball-milling medium is dehydrated alcohol, at 900 DEG C of air gas after drying Pre-burning 4 hours in atmosphere；

(3) after adding binding agent pelletize in the powder that step (2) prepares, re-compacted molding is finally big at 1200 ~ 1300 DEG C Gas atmosphere sinters 4 hours；Described binding agent uses mass concentration to be the poly-vinyl alcohol solution of 5%, the addition of polyvinyl alcohol Account for the 3% of powder gross mass.